theonenandrew

I have a 1996 F150 XL 2WD 4.9l automatic 4-spd and I've been noticing that my gas mileage has been in the single digits (~8-9mpg combined). From what I understand, I should at least be getting mid-teens in terms of mpg. I believe it's 2.73 axle ratio and it has stock wheels on it.

From the Googling I've been doing, it seems the main culprits would be O2 sensors and/or catalytic converter. One question I do have about the downstream O2 sensor is where does it plug is and is it possible to replace without having to disassemble a lot? I see the sensor but the wire goes over the trans, is there a way to reach it from the engine compartment? I don't think the cat is bad because there is no CEL on and the exhaust doesn't have a rotten smell. Would a bad/clogged cat not throw a code? Also, silly question here but how many cats are on this truck, just one?

What else could be killing the gas mileage? I don't believe any of the brakes are seized because I feel like there would be some sort of burning smell associated with that and there isn't. I've been meaning to replace to plugs and wires too since I don't know when that was done last but I can't imagine the spark plugs alone rob that much mpg, I could be wrong though. Anyway, any insight on this would be greatly appreciated! Thanks!

techrep

iTrader: (1)

You do not have an axle ratio of 2:73.. more likely 3:73 and the 02 sensor should have a plug on it or else you will need to splice it to replace.

clintm6

My truck is similar to yours, but a year older and with a 5-speed. My mileage has been as high as 19+ during the summer, but this winter it's dropped down to about 15 - 16. So winter gas could be part of your problem. I'd suggest doing all the standard "tune-up" items, like plugs, wires, fuel & air filters and see if you get any improvements. You could also do some upgrades like e-fans, hotter coil, K & N air filter, etc. to maybe squeeze a few more mpgs.

theonenandrew

Just a quick update, my gear ratio is 3.08 according to the axle code in the door frame.

I also answered my own question about the downstream O2 sensor, the wires do go up and over the trans but the connector can be reached from the opposite side (driver side) above the trans.

Thanks for the response, that was basically my plan to do all the "tune-up" type items. I do agree that winter does decrease mpg but I can't imagine that would make mine get half the mpg you get even though you have a 5-speed. I replaced the fuel and air filter just a couple months ago so next on the list is plugs, wires, and O2 sensors. Would it make sense to replace the distributor cap too?

clintm6

Yep, I'd do that too! And I notice a difference in how I drive too. I get about an extra 1 mpg going 60 instead of 65 on the highway.

Energized

I changed the fuel injectors and my mileage went from 6-7 to 12-13 on my 93 5.8, if they are stuck open and leaking it won't really matter what you do to the air filter or tire pressure, 02 sensor, plugs... etc...